Vacuum induction furnace



Feb. 21, 1961 H. J. SEEMANN ETAL 2,972,652

VACUUM INDUCTION FURNACE Filed July 30, 1958 v 5 Sheets-Sheet 1 Feb. 21, 1961 H. J. SEEMANN ETAL 2,972,652

VACUUM INDUCTION FURNACE 5 Sheets-Sheet 2 Filed July 30, 1958 IN VENTOR. 6 060 J $M4AM flaea-er M57744 75 0% r Feb. 21, 1961 H. J. SEEMANN ETAL 2,97

VACUUM INDUCTION FURNACE 5 Sheets-Sheet 3 Filed July 30, 1958 Feb. 21, 1961 H. J. SEEMANN ETAL VACUUM INDUCTION FURNACE 5 Sheets-Sheet 4 Filed July 50, 1958 INVENTORS 6060 J JfEMlA/A/ //P8er Mfr/147$ )dlm Pew Feb. 21, 1961 H. J. SEEMANN EIAL 2, 7

VACUUM INDUCTION FURNACE 5 Sheets-Sheet 5 Filed July 30, 1958 INVENTOR3 64/60 J $M4MM BY f/aeaaer WSW/17s pose of forming the wall of the vacuum chamber.

United States Patent VACUUM INDUCTION FURNACE Hugo Joseph Seemann, Saarbrucken, and Herbert Walter Staats, Neuweiler, Saar, Germany, assignors to W. C. Heraeus G.m.b.H., Hanan (Main), Germany, a corporation of Germany Filed July 30, 1958, Ser. No. 757,436

7 laims. (Cl. 13-27) The present invention relates to a vacuum induction furnace for melting metals, and more particularly to such a furnace which is provided with a primary coil around the outside of the vacuum chamber for melting the metal within a vacuum and also for carrying out a vibrational treatment of the molten metal for the purpose of attaining certain metallurgical effects.

The induction furnaces known prior to this invention had the great disadvantage that the primary coil for inducing the melting current was provided at the inside of the vacuum chamber and around the crucible. This disadvantage was prevalent particularly if electric currents of a higher frequency had to be used. On the other hand, if currents of a lower frequency were applied to these prior furnaces, it was not possible to subject the crucible and the molten material therein sufliciently to mechanical vibrations.

In order to overcome these difficulties and the disadvantages of prior induction furnaces, it is an object of the present invention to transmit high-frequency currents to the crucible within the evacuated furnace by means of a concentrating or focusing inductor to provide such an inductor at the inside of the vacuum chamber, and to mount the primary coil which supplies the high-frequency current to this concentrating or focusing inductor at the outside of the vacuum chamber.

Although similar concentrating or focusing arrangements have already been used for ordinary induction vfurnaces, they have never been used at the inside of vacuum furnaces in combination with a primary coil which supplies a high-frequency current of a high voltage to such concentrating inductor and is mounted at the out side of the vacuum chamber.

Such separation of the concentrating secondary inductor from the primary coil has the great advantage that, by mounting the latter at the outside of the vacuum chamber, there is no difiiculty in supplying the same with a high-frequency current of a high voltage and a high amperage without danger that gas discharges and electric arcs might occur between the individual coil windings or between the primary coil and the metal parts at the inside of the vacuum chamber. The present invention further avoids the necessity of high-tension conductors passing through the walls of the vacuum chamber which prior hereto caused considerable difficulties in producing and installing the same, as well as in the actual operation of the furnace. By thus being able to charge the primary coil with a very high current, it is possible to produce mechanical vibrations of adequate strength within the crucible and the metal therein, and also to supply the crucible and the metal therein with sufiicient high-frequency energy to melt the metal.

Another object of the present invention is to design the vacuum furnace in such a manner that the outer wall ,of the concentrating inductor, or more simply called .the concentrator, will be utilized for the additional pur- This has .the considerable advantage that the concentrator may be cooled very easily and effectively and that the losses in the transmission of the high-frequency from the p11:- mary coil to the concentrator will be considerably reduced.

A further object of the present invention is to design the vacuum furnace in such a manner that the outer wall of the concentrator, while being disposed at the inside of the vacuum chamber, is directly surrounded by a wall portion of the vacuum chamber which is made of an electrically nonconductive material and which carries at the outside thereof, that is, at the outside of the vacuum chamber, the primary coiliwhich is connected to th concentrator within the vacuum chamber.

A further object of the invention is to increase the efficiency and strength of the vibrations imparted to the metal contained within the crucible by combining the features of a concentrator Within the vacuum chamber and a primary coil at the outside thereof with the provision of a stationary magnetic field around the crucible. This magnetic field is preferably designed so that the lines of force thereof extend in a direction parallel to the central aXis of the crucible. According to another feature of the invention this magnetic field may be produced by designing the primary coil so as to be able to carry a high-frequency current as well as a direct current of a high intensity, and by connecting the primary coil not only to a high-frequency generator with a high output voltage, but also to a source of direct current of a high amperage. According to another embodiment of the invention, the magnetic field may also be produced by means of a special magnetizing device, the pole pieces of which also form components of the wall of the vacuum chamber, while the operating coils of the magnet are disposed at the outside of the vacuum chamber. Such magnetizing device may, however, also be provided with permanent magnets, in which event the pole pieces may likewise form parts of the wall of the vacuum chamber, while the permanent magnets for energizing the station ary magnetic field may be mounted outside of the vacuum chamber. In either case, the disadvantages which would arise if the coils or the porous permanent magnets were mounted at the inside of the vacuum chamber will be entirely avoided.

Still another object of the invention consists in providing suitable means for mechanically transmitting the vibrations to the crucible within the vacuum chamber.

For this purpose, the invention provides for the use of a vibrating crucible which is provided on its upper edge with a vibrating ring which is operatively connected to the means for transmitting the high-frequency currents and forms an element separate from the means for heating the material within the crucible inductively which are preferably provided at the lower part of the crucible. This embodiment of the invention is especially suitable for use in such cases where it is very difiicult or even impossible to heat the material within the crucible by means of a high-frequency current. The crucible may then consist of an electrically nonconductive material, or if made of a conductive material, it may be used for melting electrically nonconductive materials. In either case, the current used for melting the material may only be of a relatively low frequency. This embodiment of the invention. has the further advantage that it is relatively easy to tune the frequency of the high-frequency current used since it is no longer necessary to tune it simultaneously to a mechanical resonant frequency as well as to the electrical resonant frequency. Due to the vibrating ring, the electrical values will remain practically constant, and the frequency only needs to be tuned to the mechanical resonant frequency of the crucible and the material therein. The provision of separate means for heating inductively the melt by relatively low frequency currents has the further advantage that a sufficient stirring effect will be maintained within the melt.

According to another feature of the invention, the vibrating ring is preferably made of an electrically conductive material and it is surrounded by the inner wall of the concentrator. This results in a very high degree ofefficiency in the generation of the mechanical vibrations. The vibrating ring itself which rests upon the upper edge of the crucible may be further loaded down by a suitable weight or loading ring which maintains the vibrating ring in constant engagement with the crucible and insures the proper transmission of the mechanical vibrations produced by the vibrating ring to the molten material. 7

Finally, it is another object of the invention to transmit vibrations of a high frequency and at the greatest possible efficiency to the crucible and the material therein by providing two concentrators which are disposed in a parallel relationship to-each other and are both operatively associated with the vibrating ring on the upper edge of the crucible. For producing the stationary magnetic field in this embodiment of the invention, the pole pieces of the above-mentioned device are preferably extended to a point closely adjacent to the vibrating ring. It will thus be 'possible to produce a very strong stationary magnetic field within the vibrating ring and the adjacent area. In order to protect the pole pieces of the magnetic field-producing device from being excessively heated because of the close proximity of the crucible and the vibrating ring, as well as the loading ring, if provided, the invention further provides the surfaces of the pole pieces facing toward the crucible and the vibrating and loading rings with a suitable container through which a cooling fluid is circulated and which, if made of electrically well conductive material, will further serve as an electromagnetic screen and reduce the eddy current losses within the pole pieces.

Further objects, features, and advantages of the present invention will become apparent from the following detailed description thereof, particularly when read with reference to the accompanying drawings which illustrate by way of example several different embodiments of the invention, and in which Figure 1 shows a vertical cross section of a furnace according to the invention, taken along line I.-I of Figure 2;

Figure 2 shows a horizontal cross section taken along line IIII of Figure 1;.

Figure 3 shows a perspective view of a sealing element used in the embodiment according to Figures 1 and 2;

Figure 4 shows a vertical cross section of a furnace according to a modification of the invention;

Figure 5 shows a vertical cross section of a furnace according to another modification of the invention;

Figure 6 shows a cross section taken along line VIVI of Figure 5; while Figure 7 shows a partial vertical cross section of still another modification of the furnace according to the invention.

Referring to the drawings, and first particularly to Figures 1 and 2, the furnace according to the invention essentially consists of a vacuum chamber 1 having a bottom or base 2 and a cover 3 which is provided with an outlet 4 which is adapted to be connected to a vacuum pump, not shown. The central part of the wall of the vacuum chamber forms the outer sleeve 5 of the concentrator as previously described which is separated from bottom 2 and cover 3 by spacing rings 6 and 7 of insulating material. The joints between the individual outer parts 2 to 7 of the vacuum chamber are sealed relative to the outside by intermediate sealing rings 8 to 11. The bottom 2 of the vacuum chamber is provided with an annular flange 12 in which the crucible 13 is seated which is surrounded by the inner sleeve 14 of the concentrator. This inner sleeve 14 is connected to the outer sleeve 5 by means of electric conductors 15' so as to form a closed electric circuit through both sleeves. The outer sleeve 5 carries the primary coil 16 which surrounds sleeve 5 and is insulated therefrom by a plurality of insulating elements 17. The current for energizing the primary coil 16 is supplied thereto through the terminals 1 8 and 19. The gap 20 between the two endsof sleeve 5' is filled out by a rod-shaped sealing member 21 which may consist of rubber or a suitable plastic or better even of an inner solid element, for example, a rod or tube of metal or insulating material, which is covered with a layer of rubber. The opposite end surfaces of sleeve 5 are provided with grooves 22 in which the rod-shaped sealing member 21 is firmly seated. The area of the contact surface between these ends of sleeve 5 and sealing member 21 is thus enlarged, resulting in a better scaling action of member 21 when clamping bolts 23 which are insulated from conductors 15 by insulating washers 24 are tightened. Sealing member 21 is made of a length which is exactly equal to the height of sleeve 5 so that the upper and lower ends of both are flush with each other and these ends will then form level surfaces insuring a proper sealing action of sealing rings 9 and 16. Differences in the length or height between sealing member 21 and sleeve 5, which may be caused by changes in temperature, may be avoided by an adequate cooling of sleeve 5-. An insulating element 25 which is interposed between conductors 15 adjacent to inner sleeve 14 maintains these conductors at an adequate distance from each other.

Both concentrator sleeves 5 and 14 are provided with a water-cooling system. For this purpose, the outer sleeve 5 contains a cylindrical cooling chamber 26 which extends along almost the entire width of the sleeve, leaving upper and lower solid portions 27 and 28 on which the sealing rings 9 and 10 engage. These solid end portions of sleeve 5 insure that the current density will be slightly smaller at these points than at the central part of the sleeve so as to prevent the sleeve from inducing high-frequency currents into the bottom 2 and cover 3 of the vacuum chamber.

As illustrated in Figures 1 and 2, the cylindrical cooling chamber 26 is formed by providing an outer recess in the sleeve itself and by fitting an outer wall portion 29 up to a certain depth into this recess and then electrically connecting this wall portion to the sleeve itself, for example, by welding it thereto. The cooling water is passed into cooling chamber 26 through an inlet 30, and it is discharged therefrom through an outlet 31, which is indicated in Figure 2 in dotted lines since it would actually not be visible in this sectional view. At the inside of cooling chamber 26, deflecting plates 32 and 33 are provided. Deflecting plate 32 first directs the flow of cooling water entering chamber 26 through inlet 30 in the upward direction and substantially parallel to the point of separation between the two solid end portions 27 and 28 of sleeve 5, so that the actual circulation within cooling chamber 26 as indicated by arrows 34 will start from the upper end thereof. The other deflecting plate 33 directs the cooling water, after circulating through chamber 5 and before leaving through outlet 31 once more in the upward direction. Thus, defleeting plates 32 and 33 form inlet and outlet channels 35 and 36 in which the cooling water will flow at a relatively great speed.

These channels 35 and 36 are connected to the cooling system of the inner concentrator sleeve 14- by means of pipe conduits 37 and 38 which extend along the conductors 15 connecting the two sleeves 5 and 14. The cooling water will then flow from conduit 37 to and through a cooling ring 39 which surrounds the inner .sleeve 14 and from which it is then discharged through a conduit 31, shown in Figure 2 in dotted lines, which terminates into outlet channel 36 in the outer sleeve 5.

As also illustrated in Figures 1 and 2, the rod-shaped sealing member 21 may also be water-cooled and is for this purpose provided with a bore 41 extending in the longitudinal direction thereof, and terminating at its ends in a water inlet 42 and a water outlet 43.

The vibratory treatment of the material contained in crucible 13 may be considerably improved by providing a stationary magnetic field within crucible 13 and the material therein. The lines of force of this magnetic field should extend substantially parallel to the central axis of crucible 13. For producing the magnetic field it is possible to utilize the primary coil 16 which in this case may be designed so as to be charged not only with the high-frequency current, but also with a strong direct current.

Figure 3 illustrates perspectively the manner in which the sealing member 21, as shown in Figures 1 and 2, may be designed. The rod-shaped or tubular member 21 is preferably combined with the two sealing rings 9 and 10 which rest upon the upper and lower edges of the concentrator sleeve 5 so as to form a single unit. The outer resilient layer of member 21, which may, for example, consist of rubber, may then be continuous with the material of the sealing rings 9 and 10. By molding the sealing rings 9 and 10 in one piece with the outer sealing layer of member 21, the difiiculties of sealing the points of connection between spacing rings 6 and 7 and the outer concentrator sleeve 5 will be more easily overcome.

Figure 4 illustrates another embodiment of the invention in which the vacuum induction furnace is provided with a yoke of an electromagnet for producing a stationary magnetic field within the crucible and in the material therein. The vacuum chamber or vessel is also 'in this case provided with a bottom 46, a cover 47, while its central part is formed by upper and lower annular ferromagnetic pole pieces 48 and 49, upper and lower spacing rings of insulating material 59 and 51, and the outer concentrator sleeve 52. All of these parts are again separated from and sealed relative to each other and toward the outside by sealing rings 53 to 53. The upper pole piece 48 is integral with the upper wall 59 in which the outlet 60 is provided through which the entire vacuum chamber may be evacuated. The crucible 61 which is made of a shape especially suitable for vibration is again held within bottom 46 by being seated within a socket-like flange 62. The inner concentrator sleeve 63 is supplied with and energized by an alternating current in the same manner as described with respect to Figures 1 and 2, by means of the primary coil 64, the outer concentrator sleeve 52 and the connecting conductors 65, the gap between which is sealed by a sealing rod 65 similar to rod 21 in Figures 1 to 3. Pole pieces 48 and 49 also extend radially outwardly and are continuous with jacketlike Wall portions 66 and 67 which overlap each other and thus permit a good magnetic flux from one annular pole piece to the other. The recess formed within each pole piece 43 and 49 including its outer wall portion 66 and 67, respectively, contains an annular coil 68 and 69, respectively, which is mounted within a metallic body 70 and secured thereby to the respective pole piece, and also serves for screening off the high-frequency stray field. Suitable apertures in wall portions 66 and 67 permit the passage of the lead-ins 71 and 72 of primary coil 64. Bottom 46 which consists of ferromagnetic material is provided with a tubular extension 73 which reinforces the pole piece 49 and also permits crucible 61 together with the entire bottom element 46 to be withdrawn downwardly from the vacuum chamber. Obviously, the electromagnets as illustrated in Figure 4 may be replaced by permanent magnets.

Similarly as in the embodiment according to Figures 1 to 3, the concentrator assembly as illustrated in Figure 4 is also provided with a cooling system which consists of water coils 74 passing around the inside and 6 outside of concentrator sleeves 52 and 63, respectively. The cooling water is supplied to these coils through an inlet 75 and discharged therefrom through an outlet 76 by means of pipe conduits, not shown, passing from the inside of the magnet yoke toward the outside.

The vacuum chamber according to the further modification of the invention, as illustrated in Figures 5 and 6, is similar to the embodiment according to Figures 1 and 2 having a cover 77, a bottom or base 78, and a jacket 79, the bottom 78 supporting an insulating ring 80 which, in turn, supports the outer concentrator sleeve 81 which is spaced at a small distance from jacket 79. The inner concentrator sleeve 82 again surrounds the crucible 83 at a certain distance therefrom, while the latter is again seated within an annular flange 84 on base 78. The primary coil 85 is wound around the outside of jacket 79 of the vacuum chamber.

Similarly as in the embodiments of the invention according to Figures 1 to 4, the concentrator assembly is also in this case provided with a cooling system which consists of pipe conduits 86, the inlet 87 and the outlet 88 of which pass through jacket 79 of nonconductive material. The cooling water flows through inlet 87 into conduit 86, which first passes along the lower part of the outer concentrator sleeve 81, then around the lower part of the inner concentrator sleeve 82, then along the inside of the upper part of the outer sleeve 81, and finally around the upper part of the inner sleeve 82, from where it leads to outlet 88.

The primary coil 85 may be designed similarly as the one in the embodiment according to Figures 1 and 2 so as to be able to carry not only the high-frequency current but also a direct current of a high amperage in order to build up a stationary magnetic field, the lines of force of which extend vertically to the high-frequency currents which are induced into the crucible 83 and the material therein so that the crucible and the material will be subjected to a radial vibratory movement.

Figure 7 illustrates the essential features of a further embodiment of the invention which is somewhat similar to the one illustrated in Figure 4 but differs therefrom primarily by the fact that the high-frequency currents and the radial vibrations produced thereby are not exerted directly within the crucible and the material therein but within a separate element which is connected to the crucible. For this purpose, crucible 90 is heated by a separate induction coil 91 of a tubular construction, through which a cooling fluid is adapted to be circulated. The heating coil 91 may be supplied with a current of a lower frequency. Crucible 90 is preferably filled with the molten material in the usual manner up to a level closely underneath its upper edge 92 which has an outer upwardly projecting rim 93 with a conical inner surface 94 tapering downwardly toward the normal upper edge 92 of the crucible. This conical surface 94 is adapted .to support and center a vibrating ring 95 which is provided with an annular, downwardly projecting portion 96 of a conical shape corresponding to the shape of the surface 94. Vibrating ring 95 consists of an electrically conductive material.

The vibratory motion is again produced by a concentrator assembly and a stationary magnetic field. However, in this embodiment of the invention a double concentrator is used, that is, two concentrator assemblies which are connected in parallel and comprise the larger concentrator sleeves 97 and 98 and the inner concentrator sleeves 99 and 104). This double concentrator assembly has the advantage of being able to be supplied with currents of a higher frequency than the single concentrator assembly previously described, since the inductivity of this double assembly is considerably lower than that of a single assembly. The outer concentrator sleeves 97 and 98 are surrounded by the outer wall 101 of the vacuum chamber which, in turn, carries on its 7 outside the two primary coils 102 and 103. By this arrangement, an annular electric high-frequency current will be induced in the vibrating ring 95 of electrically conductive material. The vibrating ring 95 may be acted upon to carry out radial vibrations by being surrounded by a stationary magnetic field, the lines of force of which extend vertically to the plane of ring 95. For this purpose, pole pieces 104 and 105 are provided which extend around vibrating ring 95, similarly as shown in Figure 4.

These pole pieces 104 and 105 form parts of the outer wall of the vacuum chamber, while the magnet coils 104' and 105 respectively thereof or equivalent permanent magnets are mounted on the outside of the vacuum chamber. For sealing the vacuum chamber, pole pieces 104 and 105 are provided with recesses into which sealing rings 106 and 107, respectively, are inserted which seal the central wall portion 101 hermetically against pole pieces 104 and 105.

In order to increase the efiiciency of the vibrations, vibrating ring 95 may be provided on its upper rim with a loading or weight ring 108 which presses upon vibrating siderable heat both through its proximity to the molten material in crucible 90 and through the high-frequency currents induced therein, the double concentrator is preferably provided with a special cooling system. For this purpose, the inner concentrator sleeves 99 and100 are of a tubular shape forming pipe conduits 113 and 114, respectively, through which a cooling fluid is conducted.

iThese conduits 113 and 114 may also be extended to pass along the inside of the outer concentrating sleeves 97 and 98, and they have inlets and outlets 115 to 118, only two of which are shown, which extend through wall 101.

The pole pieces 104 and 105 may also be protected from being excessively heated by being provided at the surfaces facing toward crucible 90, vibrating ring 95,

and loading ring 108 with cooling coils 119 and 120 which are provided with an inlet and an outlet, not shown, to conduct a cooling fluid therethrough.

The double concentrator assembly as illustrated in Figure 7 may be operated either in phase or in phase opposition, the latter being especially suitable if the ire quency used lies within a resonant range of torsional vibrations of oscillating ring 95.

Although our invention has been illustrated and de.

scribed with reference to the preferred embodiments thereof, we wish to have it understood that it is in no way limited to the details of such embodiments, but is capable of numerous modifications within the scope of the appended claims.

Having thus fully disclosed our invention, what we claim is:

1. A vacuum induction furnace comprising a crucible mounted inside a vacuum chamber and constructed and arranged to contain a material to be melted, means for transmitting high-frequency electric currents to said crucible and material, said transmitting means comprising a concentrator assembly mounted inside the vacuum chamber and a primary coil mounted outside the vacuum chamber, said concentrator assembly including an outer concentrator sleeve means and an inner concentrator sleeve means surrounding and adjacent the crucible, and means for producing a stationary magnetic field Within the area of the crucible and the material therein.

2. A vacuum induction furnace comprising a crucible mounted inside a vacuum chamber and constructed and arranged to contain a material to be melted, said crucible being designed to vibrate and including a vibrating ring of electrically conductive material resting on an upper edge of the crucible and a loading ring resting on the vibrating ring to maintain the vibrating ring in constant engagement with the upper edge of the crucible, means for transmitting high-frequency electric currents to said crucible and material, said transmitting means being operatively associated with the vibrating ring and comprising a concentrator assembly mounted inside the vacuum chamber and a primary coil mounted outside the vacuum chamber, said concentrator assembly including an outer concentrator sleeve means and an inner concentrator sleeve means surrounding and adjacent the crucible, and means for producing a stationary magnetic field within the area of the crucible and the material therein.

3. The vacuum induction furnace of claim 2, wherein the lines of force of said magnetic field extend in a direction vertical to the direction of the high-frequency currents induced in said vibrating ring and substantially parallel to the central axis of the crucible.

. 4. The vacuum induction furnace of claim 3, wherein the innerconcentrator sleeve means surrounds the vibrating ring of the crucible. I

5. A vacuum induction furnace comprising a crucible mounted inside a vacuum chamber and constructed and arranged to contain a material to be melted, said crucible being designed to vibrate and including a vibrating ring of electrically conductive material resting on an upper edge of the crucible and a loading ring resting on the vibrating ring to maintain the vibrating ring in constant engagement with the upper edge of the crucible, means for transmitting high-frequency electric currents to said crucible and material, said transmitting means being operatively associated with the vibrating ring and comprising a concentrator assembly mounted inside the vacuum chamber and a primary coil mounted outside the vacuum chamber, said concentrator assembly including a pair of parallel outer concentrator sleeves and a pair of inner concentrator sleeves surrounding the vibrating ring, and means for producing a stationary magnetic field within the area of the vibrating ring, the lines of force of said magnetic field extending in a direction vertical to the direction of the high-frequency currents induced in said vibrating ring and substantially parallel to the central axis of the crucible.

6. The vacuum induction furnace of claim 5, wherein the two inner concentrator sleeves are tubular members constructed and arranged to pass a cooling fluid there- 'through.

7. The vacuum induction furnace of claim 6, wherein 'each outer concentrator sleeve is a generally annular member with two adjacent ends separated by a gap and a rod-shaped sealing member is positioned in said gap, the outer sleeves forming at least part of a hermetically sealed outer Wall of said vacuum chamber.

References Cited in the file of this patent 

